ScienceDaily (May 15, 2008) — Women who have a sister diagnosed with breast cancer are at an increased risk of developing the disease throughout their lives. The increased risk is most pronounced in younger women, regardless of the age at which the first sister was diagnosed.

Women who have a first degree relative affected by breast cancer are at increased risk for the disease, but it is unclear how a woman's risk varies with her current age and the age at which her relative was diagnosed.

To find out, Marie Reilly, Ph.D., and colleagues at the Karolinska Institute in Stockholm analyzed a national family database that is linked to the national cancer register. They compared the breast cancer incidence between 1958 and 2001 in 23,654 sisters of breast cancer patients and in 1,732,775 women who did not have a sister with breast cancer.

The familial risk was highest for young women, aged 20 to 39, with a 6.6-fold increase in the risk of breast cancer diagnosis, compared with similarly aged women who did not have a sister with breast cancer. The excess risk declined to approximately two-fold for women aged 50 and older. For the sisters of a breast cancer patient, the risk of diagnosis was similar regardless of whether she was approaching the age at which her sister had been diagnosed or had already passed it.

"Sisters of women diagnosed with breast cancer still have an increased risk of breast cancer 20 years after diagnosis of the sister, suggesting that women live with the burden of familial breast cancer for their lifetime," the authors write.

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Adapted from materials provided by Journal of the National Cancer Institute, via EurekAlert!, a service of AAAS.

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